With the concern regarding promoting non-rainbow decks.
I would suggest, rather than further destroying the effectiveness of rainbows, promote non-rainbow deck building.
As a newbie I am having a tough time building an efficient deck. Some of the best (affordable for newbies) farming decks (level 3, top 50) are non-rainbow, or speed decks. These are not always effective to start upgrading with the aim on false god challenging.
In order to help level the playing field with tougher challenges facing new players today (in deck building), I would propose altering the cost for upgrading mono producing pillars only. If quantum pillars produce 3 quanta, and cost 1500 to upgrade (a fair cost) then it stands to my reasoning that mono producing pillars should perhaps cost 1/3 (500 coins?) of the cost of the more popular quantum towers.
I believe this would help offset the increased difficulty in version 1.21 for a new member (tougher AI & FG not to mention fully upgraded decks in top 50) to begin to dream of challenging the tougher decks before despair begins to set in, and interest is lost in an awesome game.
Kudos to the developer and all the contributors that have made Elements great.
This is just my suggestion for improving the enjoyment for newer players. Thanks.